Fabrication of lignin-based sub-micro hybrid particle as a novel support for adenylate cyclase immobilization

This study developed a surface functionalized lignin-based sub-microsphere as an innovative support for enzyme immobilization. Lignin was first modified with a silane reagent leading to lignin/SiO2 (LS) organic/inorganic hybrid particles, displayed as regular sub-micro spheres with a SiO2 shell as demonstrated in SEM images. The LS particles were further modified to introduce nickel ions, as evidenced in XPS spectra, facilitating affinity adsorption with a his-tagged enzyme. The immobilization of adenylate cyclase from Haloactinopolyspora alba (HaAC), expressed in Escherichia coli, was conducted on the surface functionalized LS (LS-G-NTA-Ni). The immobilization conditions were optimized to achieve the highest relative activity, which were determined to be using a Ni2+ concentration of 62.5 mM, at pH=9.5 and 25 °C, with an enzyme-to-support ratio of 4.0 for a duration of 2 h. The immobilized HaAC shows maximum relative activity at pH=9.5 and 40 °C, and exhibits significantly improved thermal stability compared to the free enzyme. After undergoing five reusing cycles, the immobilized HaAC maintains a satisfactory activity (54.15%), which is due to the surface chemistry and the structural stability of the functionalized LS. This work provides a valuable exploration for high-value application of industrial lignin.

Metal Oxides Nanomaterials and Nanocomposite-Based Electrochemical Sensors for Healthcare Applications

Wide-ranging research efforts have been directed to prioritize scientific and technological inventions for healthcare monitoring. In recent years, the effective utilization of functional nanomaterials in various electroanalytical measurements realized a rapid, sensitive, and selective detection and monitoring of a wide range of biomarkers in body fluids. Owing to good biocompatibility, high organic capturing ability, strong electrocatalytic activity, and high robustness, transition metal oxide-derived nanocomposites have led to enhancements in sensing performances. The aim of the present review is to describe key advancements of transition metal oxide nanomaterials and nanocomposites-based electrochemical sensors, along with current challenges and prospects towards the development of a highly durable and reliable detection of biomarkers. Moreover, the preparation of nanomaterials, electrode fabrication, sensing mechanism, electrode-bio interface, and performance of metal oxides nanomaterials and nanocomposite-based sensor platforms will be described.

Rationally designed NiMn LDH@NiCo2O4core-shell structures for high energy density supercapacitor and enzyme-free glucose sensor

Exploring high-efficiency and low-cost bifunctional electrodes for supercapacitors and sensors is significant but challenging. Most of the existing electrodes are mostly single-functional materials with simple structure. Herein, NiCo₂O₄nanowires as the core and NiMn layered double hydroxide (LDH) as the shell is directly grownin situon carbon cloth (CC) to form a heterostructure (NiMn LDH@NiCo₂O₄/CC). The performance in supercapacitors and enzyme-free glucose sensing has been systematically studied. Compared with a single NiCo₂O₄nanowire or NiMn LDH nanosheet, the heterogeneous interface produced by the unique core-shell structure has stronger electronic interaction and abundant active surface area, which shows excellent electrochemical performance. Electrochemical tests demonstrate that the NiMn LDH@NiCo₂O₄/CC core-shell electrode possesses an area specific capacitance of 2.40 F cm^-2and a rate capability of 76.22% at 20 mA cm^-2. Simultaneously, asymmetric supercapacitor is assembled with it as the positive electrode and NiFe LDH@NiCo₂O₄/CC as the negative electrode. The supercapacitor possesses an energy density of 47.74 Wh kg^-1when the power density is 175 W kg^-1, revealing excellent performance and maintains cycle stability of 93.48% after 6000 cycles at 10 mA cm^-2. Additionally, the electrode applied as enzyme-free glucose sensor electrode also displays outstanding sensitivity of 2139μA mM^-1cm^-2, wide detection range (2μM^-3mM and 4-8 mM) and low detection limit of 210 nM, representing good anti-interference performance. This work reveals the multi-metal synergy and rationally designed core-shell structure is critical to the electrochemical performance of bifunctional electrodes.

Construction of an MnO2 nanosheet array 3D integrated electrode for sensitive enzyme-free glucose sensing

MnO₂ based electrochemical enzyme-free glucose sensors remain significantly limited by their low electronic conductivity and associated complex preparation. In this paper, an MnO₂ nanosheet array supported on nickel foam (MnO₂ NS/NF) was prepared using a simple hydrothermal synthesis and employed as a 3D integrated electrode for enzyme-free glucose detection. It was found that MnO₂ NS/NF shows high performance with a wide linear range from 1 μM to 1.13 mM, a high sensitivity of 6.45 mA mM^-1 cm^-2, and a low detection limit of 0.5 μM (S/N = 3). Besides, MnO₂ NS/NF shows high selectivity against common interferences and good reliability for glucose detection in human serum. This work demonstrates the promising role of MnO₂ NS/NF as an efficient integrated electrode in enzyme-free glucose detection with high performance.

A facile synthesis of CoMn2O4 nanosheets on reduced graphene oxide for non-enzymatic glucose sensing

A non-enzymatic sensor nanomaterial which is composed of ultra-thin scaly CoMn₂O₄ nanosheets grown on the surface of reduced graphene oxide sheets (CoMn₂O₄ NSs/rGO) has been successfully synthesized by a simple method for glucose sensing. The morphology and elemental composition of CoMn₂O₄ NSs/rGO are researched by means of x-ray diffraction, field emission scanning electron microscope, and transmission electron microscope. Cyclic voltammetry and amperometry are used to analyse the glucose oxidation characteristics of the material. The test results show that the non-enzymatic glucose sensor based on CoMn₂O₄ NSs/rGO has excellent glucose sensing performance, exhibiting a wide linear range of 0.1-30 mM with high sensitivity of 6830.5 μA mM^-1 cm^-2, which is better than other glucose sensors. In addition, the CoMn₂O₄ NSs/rGO sensor has superior anti-interference and stability. More importantly, the sensor can be applied to the measurement of real sample, which makes it have the potential to become a reliable clinical glucose sensor.

Facile synthesis of CuCo2O4@NiCo2O4 hybrid nanowire arrays on carbon cloth for a multicomponent non-enzymatic glucose sensor

The design of hierarchical heterogeneous structures with rational components is considered as a promising method to enhance the properties of electrocatalyst. Binary metal oxides, with high electrochemical activity, have attracted considerable interest in glucose determination. In this work, we synthesized the CuCo₂O₄@NiCo₂O₄ hybrid structure on conductive carbon cloth (CC) via a simple two-step hydrothermal process and investigated its catalytic ability toward glucose. The two individual components that make up this hybrid electrode have good electrical conductivity and excellent catalytic properties for glucose, so the smart combination of these two active materials can provide more catalytic sites and sufficient redox couples for the glucose oxidation. As a result, the CuCo₂O₄@NiCo₂O₄ modified CC presented superior glucose sensing properties, including ultrahigh sensitivity, fast response time, wide linear range and acceptable detection limit. Besides, the sample also exhibited good selectivity for substances in human blood that interfere with glucose detection, such as UA, AA, fructose, sucrose and KCl. The potential of the CuCo₂O₄@NiCo₂O₄/CC electrode for practical application was investigated by measuring the glucose concentration in real serum samples. These results prove that the construction of hierarchical ordered structure is conducive to the improvement of glucose sensor.

Nickel sulfide-incorporated sulfur-doped graphitic carbon nitride nanohybrid interface for non-enzymatic electrochemical sensing of glucose

A nickel sulfide-incorporated sulfur-doped graphitic carbon nitride (NiS/S-g-C₃N₄) nanohybrid was utilized as an interface material for the non-enzymatic sensing of glucose in an alkaline medium (0.1 M NaOH). The precursors used in the preparation of NiS/S-g-C₃N₄ hybrid were thiourea and nickel nitrate hexahydrate as the sulfur and nickel sources, respectively. The HRTEM results reveal that NiS nanoparticles incorporated on the S-g-C₃N₄ nanosheet surface could enhance the electrocatalytic activity and electrical conductivity. The prepared NiS/S-g-C₃N₄ crystalline nature, surface functionalities, graphitic nature, thermal stability and surface composition were investigated using XRD, FT-IR, Raman spectroscopy, TGA and XPS analyses. The NiS/S-g-C₃N₄ modified electrode was used for the non-enzymatic sensing of glucose at an applied potential of 0.55 V vs. Ag/AgCl with a detection limit of 1.5 μM (S/N = 3), sensitivity of 80 μA mM^-1 cm^-2 and the response time of the fabricated sensor was close to 5 s. Different inorganic ions and organic substances did not interfere during glucose sensing. The NiS/S-g-C₃N₄ nanohybrid material could be extended for a real sample analysis and open the way for diverse opportunities in the electrochemical sensing of glucose.

NiCo2O4 Nano-/Microstructures as High-Performance Biosensors: A Review

Non-enzymatic biosensors based on mixed transition metal oxides are deemed as the most promising devices due to their high sensitivity, selectivity, wide concentration range, low detection limits, and excellent recyclability. Spinel NiCo2O4 mixed oxides have drawn considerable attention recently due to their outstanding advantages including large specific surface area, high permeability, short electron, and ion diffusion pathways. Because of the rapid development of non-enzyme biosensors, the current state of methods for synthesis of pure and composite/hybrid NiCo2O4 materials and their subsequent electrochemical biosensing applications are systematically and comprehensively reviewed herein. Comparative analysis reveals better electrochemical sensing of bioanalytes by one-dimensional and two-dimensional NiCo2O4 nano-/microstructures than other morphologies. Better biosensing efficiency of NiCo2O4 as compared to corresponding individual metal oxides, viz. NiO and Co3O4, is attributed to the close intrinsic-state redox couples of Ni3+/Ni2+ (0.58 V/0.49 V) and Co3+/Co2+ (0.53 V/0.51 V). Biosensing performance of NiCo2O4 is also significantly improved by making the composites of NiCo2O4 with conducting carbonaceous materials like graphene, reduced graphene oxide, carbon nanotubes (single and multi-walled), carbon nanofibers; conducting polymers like polypyrrole (PPy), polyaniline (PANI); metal oxides NiO, Co3O4, SnO2, MnO2; and metals like Au, Pd, etc. Various factors affecting the morphologies and biosensing parameters of the nano-/micro-structured NiCo2O4 are also highlighted. Finally, some drawbacks and future perspectives related to this promising field are outlined.

In situ formation of Co3O4 hollow nanocubes on carbon cloth-supported NiCo2O4 nanowires and their enhanced performance in non-enzymatic glucose sensing

Diabetes is a chronic disease that can seriously affect human health. Therefore it is important to develop a rapid and highly sensitive enzyme-free glucose sensor to aid the treatment of diabetes. In this work, homogeneous NiCo₂O₄ nanowire arrays were synthesized in an orderly fashion on flexible carbon cloth (CC) by a facile hydrothermal method. Then well-structured zeolitic imidazolate framework (ZIF-67) nanocubes were grown in situ on the as-prepared NiCo₂O₄ nanowires to form a hybrid nanoarchitecture. The hierarchical structure was transformed into a Co₃O₄/NiCo₂O₄/CC composite after annealing in the air. The as-prepared electrode was put into 0.1 M NaOH, and cyclic voltammetry and amperometry were employed to investigate its electrocatalytic properties at room temperature. It was found that the Co₃O₄/NiCo₂O₄/CC electrode exhibited outstanding sensing properties towards glucose, including terrific sensitivity (12.835 mA mM^-1 cm^-2), a wide linear range (from 1 μM to 1.127 mM), a low detection limit (0.64 μM) and a fast response time (within 2 s). In addition, it also had excellent selectivity, reproducibility and stability. The improvement in enzyme-free glucose sensing, in addition to the high porosity and large specific surface area of metal organic framework-derived Co₃O₄ hollow nanocubes, can be attributed to the NiCo₂O₄ nanowire arrays affording fast channels for electron transfer between CC and Co₃O₄. Accordingly, this method, which directly prepares hierarchical composite nanomaterials on a conductive substrate, may open up a new perspective for the enhancement of non-enzymatic glucose-sensing properties.

A bio-inspired highly selective enzymatic glucose sensor using a red blood cell membrane

Red blood cell membrane (RBCM) was coated onto the enzymatic glucose sensor. The permeability of RBCM was optimized by controlling the thickness. Intriguingly, the sensor was highly accurate, despite the existence of various interfering molecules.

Fabrication of porous NiMn2O4 nanosheet arrays on nickel foam as an advanced sensor material for non-enzymatic glucose detection

In this work, porous NiMn₂O₄ nanosheet arrays on nickel foam (NiMn₂O₄ NSs@NF) was successfully fabricated by a simple hydrothermal step followed by a heat treatment. Porous NiMn₂O₄ NSs@NF is directly used as a sensor electrode for electrochemical detecting glucose. The NiMn₂O₄ nanosheet arrays are uniformly grown and packed on nickel foam to forming sensor electrode. The porous NiMn₂O₄ NSs@NF electrode not only provides the abundant accessible active sites and the effective ion-transport pathways, but also offers the efficient electron transport pathways for the electrochemical catalytic reaction by the high conductive nickel foam. This synergy effect endows porous NiMn₂O₄ NSs@NF with excellent electrochemical behaviors for glucose detection. The electrochemical measurements are used to investigate the performances of glucose detection. Porous NiMn₂O₄ NSs@NF for detecting glucose exhibits the high sensitivity of 12.2 mA mM⁻¹ cm⁻² at the window concentrations of 0.99–67.30 μM (correlation coefficient = 0.9982) and 12.3 mA mM⁻¹ cm⁻² at the window concentrations of 0.115–0.661 mM (correlation coefficient = 0.9908). In addition, porous NiMn₂O₄ NSs@NF also exhibits a fast response of 2 s and a low LOD of 0.24 µM. The combination of porous NiMn₂O₄ nanosheet arrays and nickel foam is a meaningful strategy to fabricate high performance non-enzymatic glucose sensor. These excellent properties reveal its potential application in the clinical detection of glucose.

A novel method to construct a 3D FeWO4 microsphere-array electrode as a non-enzymatic glucose sensor

As the special sensor for glucose detection, a non-noble-metal nanoarray architecture is extremely attractive due to its easy accessibility to target molecules and more exposed surface area. In this communication, we report the first synthesis of FeWO₄ microsphere-array on the three-dimensional (3D) Ni foam (FeWO₄ microspheres/NF) as the mimetic electrode for efficient catalytic oxidation of glucose in an alkaline medium. When used as an artificial analog glucose sensor, the result of the present sensing system can also be calculated with a sensitivity of 2810 μA mM cm^-2, a linear range from 0.04 mM to 2 mM and a detection limit up to 1.4 μM (S/N = 3). This glucose sensor with satisfactory stability and reproducibility can also be applied to the detection of glucose in human serum. As a promising sensing platform, this proposed 3D FeWO₄ microspheres/NF may open a new strategy for pursuing electrochemical detection of biomolecules.

High-performance electrochemical nitrite sensing enabled using commercial carbon fiber cloth

Exceptional high-performance and stable electrochemical nitrite sensing enabled using commercial carbon fiber cloth.